The metastasis of malignant tumors to the oral cavity remains a rare clinical entity. Most metastatic tumors have the propensity for involving the mandible rather than the oral soft tissues. Herein, we describe an unusual case of ovarian mucinous cystadenocarcinoma that metastasized to the mandibular gingiva as an initial manifestation. There is little information regarding metastatic ovarian cancer to the oral cavity. A patient was a 54-year-old woman who developed the paresthesia and swelling of the right mandible after tooth extraction. A pantomograph revealed an osteolytic lesion in the right mandible. A biopsy taken from the gingiva showed mucinous adenocarcinoma, indicating the gingival metastasis of undiscovered primary cancer. A positron emission tomography and computed tomography using 18F-fluorodeoxyglucose depicted an ovarian tumor with multiple pelvic and paraaortic lymph node swellings. A magnetic resonance imaging (MRI) clearly demonstrated the presence of an ovarian cancer. Based on the imaging studies, the diagnosis of the gingival metastasis of an ovarian cancer was suspected. Serum CEA levels were elevated at 125.6 ng/ml (normal range, 0 - 5 ng/ml). She underwent the right segmental mandiblectomy with functional neck dissection and left salpingo-oophorectomy. The histology of surgical specimen confirmed the gingival metastasis of ovarian mucinous adenocarcinoma. Neoplastic cells in the gingiva infiltrated to the mandibular bone. She has been treated with adjuvant chemotherapy consisting of paclitaxel and carboplatin. This case emphasizes that although rare, metastatic ovarian cancer to the gingiva should be included in the differential diagnosis of tumors in the oral cavity.